Casting vs. Machining Drawing

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Casting vs. Machining Drawing

Casting vs. Machining Drawing

I am looking for some information regardng the differences between casting drawings and machining drawings. Specfically, what kind of tolerances are associated with various casting processes versus a machining process? Also, if I have a part that needs a casting and machining drawing made for it, how would I reflect this difference in Solidworks? Any help would be greatly appreciated.

Thank you

RE: Casting vs. Machining Drawing

To start with, if you're having to ask these sorts of questions, I'm not really sure that you should be creating Casting and/or Machining drawings.

And besides, since you're asking this question in what appears to be the context of Solidworks, you may get better answers if you were to post this question in the Eng-Tips Forum dedicated to Solidworks.

RE: Casting vs. Machining Drawing

TO begin with you need to refer ASM Metals Handbook Volume 15 -Casting. After you have understood the design parameters and limitations of the process,you could progress towards Solidworks. Else, as John hinted it will end up as a student assignment.

_____________________________________"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

This will give you some guidelines on how to create drawings for cast parts, including the subsequent machining drawing.

It will not give you information on tolerance values, this is derived per Mint.

However, if you want process capability type tolerance information you may have to talk to individual vendors. Sometimes industry associations have guidelines (maybe the source Arunmmrao mentions) or sometimes reference books but they'll typically be fairly general and you'll often get more specific answers from actual foundries. Also as you hint, there are many different casting processes and each has it's own strengths and weaknesses when it comes to tolerance capabilities and related issues.

Some places have design guides on line that you can look at. For instance I've used A.L. Johnson for Rubber Plaster Mold Aluminum castings they have some info online http://www.aljcast.com/prod.html and I was able to get much more information from their free casting design kit.

(This is the wrong place for the Solid Works part of the question, however I'll have to disagree with John about the entire question belonging there - this is a reasonable place for the non CAD part of the question. There are also dedicated drafting & casting forums for those aspects.)

RE: Casting vs. Machining Drawing

The way I approach this from a modeling perspective is to make the casting model first, merge the casting into my machined part model as the first solid and then make only material removal features in the machined part. That way you are sure that what you end up with is geometrically correct. Some people do it the other way around, make the machined part and then add material for the casting part.

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RE: Casting vs. Machining Drawing

Thank you Kenat and dgallup for the info. Kenat is correct that my question is half non-CAD/half CAD and should have been partly asked on the Solidworks forum. I will look into getting the ASME standards for Castings as Kenat suggested. This was to primarily increase my understanding of what guidelines to follow when modeling something for casting and machining purposes. I greatly appreciate the link to A.L. Johnson's site (from Kenat), as I was able to see from a tolerance standpoint what should go into a casting part design. To follow up on what dgallup suggested, I will make two configurations in Solidworks; one for the casting model and one for machining model and link the corresponding drawings to each model.

RE: Casting vs. Machining Drawing

In some eras and in some industries the foundry was given the drawing of the finished part and they create a drawing of what the finished casting should look like, and of course the pattern needed to create the cast part.

RE: Casting vs. Machining Drawing

Just remember, the info from A L Johnson only applies to their process and the materials they can handle. It is not a typical casting process so don't try and extrapolate it to other applications.

If their process suits your volume, size, material (etc.) requirements then I'd contact them to get the full guide - there's a lot in it - I spent a couple of evenings going over it last year when I was designing a part.

RE: Casting vs. Machining Drawing

Adding to T Moose's comment.The company I used to work at in the UK had a foundry attached. we would give them a drawing of the finished part. The pattern makers would then create molds for the finished part using an expansion rule. This device was a rule calibrated for the expected shrinkage of that metal as it cooled. A common nasty practical joke was to lend that rule to a machinist.B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

RE: Casting vs. Machining Drawing

"In some eras and in some industries the foundry was given the drawing of the finished part and they create a drawing of what the finished casting should look like, and of course the pattern needed to create the cast part."

Well and good, when the foundry understands the design constraints of the finished part.

RE: Casting vs. Machining Drawing

Besides the excellent guidance provided in some of the previous posts, I'd offer this perspective on engineering drawings in general. An engineering drawing, such as those for your cast part and machined part, is a set of requirements for a finished part condition. The drawing should define those requirements as completely and specifically as possible, since anything not defined on the drawing is left open to your supplier's discretion. Castings usually have a separate part number from the finish machined part, because raw castings are commonly supplied by outside vendors.

In the current digital age, it is common to use a 3D CAD model as the basis for the physical definition of the part. Thus, ideally the CAD model of the casting would include all of the relevant features in the cast part as delivered. This means draft, fillets, core supports, tooling points, parting lines, etc. The foundry will add features like risers, gates, etc. to your model, and they will also scale the model with the appropriate shrinkage factor to produce the pattern or mold tooling.

Hope that helps.Terry

RE: Casting vs. Machining Drawing

It is not a typical casting process so don't try and extrapolate it to other applications.. I endorse the statement by Kenat. I had a look at their site and the details provided are not complete or comprehensive. They do not specify the alloy,sand,investment or die cast etc.

It is just a first iterative step towards developing a solid product from a drawing. Handbook on casting will be a good place to start in my opinion.

_____________________________________"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

RE: Casting vs. Machining Drawing

arunmrao - their design guide (which there is a button on their site to ask for) has much of that information in. In fact Arunmrao, I thought that their site made it clear they only do Rubber Plaster Molding, though I haven't been on there in a while.